In order to improve tensile strength, flexural strength, and impact strength of a polyolefin resin such as polypropylene and the like, methods of adding rigid reinforcement such as other polymer resins, rubber components, or inorganic fillers and the like are used. However, adding of general reinforcement materials could not sufficiently improve mechanical properties, and compatibilizers used to uniformly mix them with the polyolefin resin were not suitable for wide use because they are relatively expensive.
Recently, in order to apply a polypropylene resin for automobile parts and electrical/electronic parts, inorganic fillers such as glass fiber, talc, whiskers, glass bubbles, and the like have been extensively used as a rigid reinforcement.
For example, Korean Registered Patent No. 1147386 (Patent Document 1) discloses a resin composition including a polyolefin-based resin, inorganic fillers, glass bubbles, and ionomers functioning as a compatibilizer. However, in Patent Document 1, the polyolefin and glass bubbles are mixed using a twin screw [0018] extruder to prepare a polypropylene composite resin composition, however, when the polymer resin and glass bubbles are simply mixed and extruded, it may be difficult to maintain the shape of the glass bubbles and the effect of improving properties resulting from the use of glass bubbles may not be so significant.
Further, Korean Laid-Open Patent Publication No. 2013-0135519 (Patent Document 2) discloses a method of using equipment performing a continuous process of an extruder and an injection machine in order to increase impregnability and compatibility between a polyolefin resin and inorganic fillers such as glass fiber, glass bubbles, and the like. However, even by this method, the shape of the glass fiber and glass bubbles may be changed in the extrusion and injection processes, and glass bubbles located inside the polymer resin may be pulverized to form pores at those parts, thus degrading the properties of the final product.
Recently, methods of using an aerogel or air-gel are being introduced in the fields of insulating materials, shock absorbers, soundproof materials, and the like. The aerogel is characterized by a structure consisting of entangled microfilaments with a thickness of about 1 ten thousandths of that of a hair and a porosity of 90% or more, and the main material thereof is silicon oxide, carbon, or an organic polymer. Particularly, the aerogel is a very low density material having high light transmittance and very low thermal conductivity due to the above-explained structural characteristics. However, since the aerogel has very weak strength such as being easily broken by a small impact due to high brittleness and is difficult to process in various thicknesses and shapes, it had a limitation for application as an insulating material despite its excellent insulation property, and in case an aerogel and other reactants are mixed, a polymer resin may permeate inside the aerogel to increase the viscosity of the compound, making mixing impossible, and thus complexation or use in combination with other materials is difficult, and it cannot exhibit the properties of a porous aerogel.
Particularly, the aerogel had problems in that it does not have high compatibility with a polymer resin or the shape is changed or destroyed in the process of mixing with a polymer resin, and thus various methods of mixing a polymer resin and an aerogel have been attempted.